commons-rng-core/src/main/java/org/apache/commons/rng/core/source64/L64X128Mix.java - commons-rng - Git at Google

 /*
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
  * The ASF licenses this file to You under the Apache License, Version 2.0
  * (the "License"); you may not use this file except in compliance with
  * the License.  You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package org.apache.commons.rng.core.source64;

 import java.util.stream.Stream;
 import org.apache.commons.rng.SplittableUniformRandomProvider;
 import org.apache.commons.rng.UniformRandomProvider;
 import org.apache.commons.rng.core.util.RandomStreams;

 /**
  * A 64-bit all purpose generator.
  *
  * <p>This is a member of the LXM family of generators: L=Linear congruential generator;
  * X=Xor based generator; and M=Mix. This member uses a 64-bit LCG and 128-bit Xor-based
  * generator. It is named as {@code "L64X128MixRandom"} in the {@code java.util.random}
  * package introduced in JDK 17; the LXM family is described in further detail in:
  *
  * <blockquote>Steele and Vigna (2021) LXM: better splittable pseudorandom number generators
  * (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5,
  * Article 148, pp 1–31.</blockquote>
  *
  * <p>Memory footprint is 256 bits and the period is 2<sup>64</sup> (2<sup>128</sup> - 1).
  *
  * <p>This generator implements
  * {@link org.apache.commons.rng.LongJumpableUniformRandomProvider LongJumpableUniformRandomProvider}.
  * In addition instances created with a different additive parameter for the LCG are robust
  * against accidental correlation in a multi-threaded setting. The additive parameters must be
  * different in the most significant 63-bits.
  *
  * <p>This generator implements
  * {@link org.apache.commons.rng.SplittableUniformRandomProvider SplittableUniformRandomProvider}.
  * The stream of generators created using the {@code splits} methods support parallelisation
  * and are robust against accidental correlation by using unique values for the additive parameter
  * for each instance in the same stream. The primitive streaming methods support parallelisation
  * but with no assurances of accidental correlation; each thread uses a new instance with a
  * randomly initialised state.
  *
  * @see <a href="https://doi.org/10.1145/3485525">Steele &amp; Vigna (2021) Proc. ACM Programming
  *      Languages 5, 1-31</a>
  * @see <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/random/package-summary.html">
  *      JDK 17 java.util.random javadoc</a>
  * @since 1.5
  */
 public class L64X128Mix extends AbstractL64X128 implements SplittableUniformRandomProvider {
     /**
      * Creates a new instance.
      *
      * @param seed Initial seed.
      * If the length is larger than 4, only the first 4 elements will
      * be used; if smaller, the remaining elements will be automatically
      * set. A seed containing all zeros in the last two elements
      * will create a non-functional XBG sub-generator and a low
      * quality output with a period of 2<sup>64</sup>.
      *
      * <p>The 1st element is used to set the LCG increment; the least significant bit
      * is set to odd to ensure a full period LCG. The 2nd element is used
      * to set the LCG state.</p>
      */
     public L64X128Mix(long[] seed) {
         super(seed);
     }

     /**
      * Creates a new instance using a 4 element seed.
      * A seed containing all zeros in the last two elements
      * will create a non-functional XBG sub-generator and a low
      * quality output with a period of 2<sup>64</sup>.
      *
      * <p>The 1st element is used to set the LCG increment; the least significant bit
      * is set to odd to ensure a full period LCG. The 2nd element is used
      * to set the LCG state.</p>
      *
      * @param seed0 Initial seed element 0.
      * @param seed1 Initial seed element 1.
      * @param seed2 Initial seed element 2.
      * @param seed3 Initial seed element 3.
      */
     public L64X128Mix(long seed0, long seed1, long seed2, long seed3) {
         super(seed0, seed1, seed2, seed3);
     }

     /**
      * Creates a copy instance.
      *
      * @param source Source to copy.
      */
     protected L64X128Mix(L64X128Mix source) {
         super(source);
     }

     /** {@inheritDoc} */
     @Override
     public long next() {
         // LXM generate.
         // Old state is used for the output allowing parallel pipelining
         // on processors that support multiple concurrent instructions.

         final long s0 = x0;
         final long s = ls;

         // Mix
         final long z = LXMSupport.lea64(s + s0);

         // LCG update
         ls = M * s + la;

         // XBG update
         long s1 = x1;

         s1 ^= s0;
         x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b
         x1 = Long.rotateLeft(s1, 37); // c

         return z;
     }

     /** {@inheritDoc} */
     @Override
     protected L64X128Mix copy() {
         // This exists to ensure the jump function performed in the super class returns
         // the correct class type. It should not be public.
         return new L64X128Mix(this);
     }

     /** {@inheritDoc} */
     @Override
     public SplittableUniformRandomProvider split(UniformRandomProvider source) {
         return create(source.nextLong(), source);
     }

     /** {@inheritDoc} */
     @Override
     public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) {
         return RandomStreams.generateWithSeed(streamSize, source, L64X128Mix::create);
     }

     /**
      * Create a new instance using the given {@code seed} and {@code source} of randomness
      * to initialise the instance.
      *
      * @param seed Seed used to initialise the instance.
      * @param source Source of randomness used to initialise the instance.
      * @return A new instance.
      */
     private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) {
         // LCG state. The addition uses the input seed.
         // The LCG addition parameter is set to odd so left-shift the seed.
         final long s0 = seed << 1;
         final long s1 = source.nextLong();
         // XBG state must not be all zero
         long x0 = source.nextLong();
         long x1 = source.nextLong();
         if ((x0 | x1) == 0) {
             // SplitMix style seed ensures at least one non-zero value
             x0 = LXMSupport.lea64(s1);
             x1 = LXMSupport.lea64(s1 + LXMSupport.GOLDEN_RATIO_64);
         }
         return new L64X128Mix(s0, s1, x0, x1);
     }
 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package org.apache.commons.rng.core.source64;

	import java.util.stream.Stream;
	import org.apache.commons.rng.SplittableUniformRandomProvider;
	import org.apache.commons.rng.UniformRandomProvider;
	import org.apache.commons.rng.core.util.RandomStreams;

	/**
	* A 64-bit all purpose generator.
	*
	* <p>This is a member of the LXM family of generators: L=Linear congruential generator;
	* X=Xor based generator; and M=Mix. This member uses a 64-bit LCG and 128-bit Xor-based
	* generator. It is named as {@code "L64X128MixRandom"} in the {@code java.util.random}
	* package introduced in JDK 17; the LXM family is described in further detail in:
	*
	* <blockquote>Steele and Vigna (2021) LXM: better splittable pseudorandom number generators
	* (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5,
	* Article 148, pp 1–31.</blockquote>
	*
	* <p>Memory footprint is 256 bits and the period is 2<sup>64</sup> (2<sup>128</sup> - 1).
	*
	* <p>This generator implements
	* {@link org.apache.commons.rng.LongJumpableUniformRandomProvider LongJumpableUniformRandomProvider}.
	* In addition instances created with a different additive parameter for the LCG are robust
	* against accidental correlation in a multi-threaded setting. The additive parameters must be
	* different in the most significant 63-bits.
	*
	* <p>This generator implements
	* {@link org.apache.commons.rng.SplittableUniformRandomProvider SplittableUniformRandomProvider}.
	* The stream of generators created using the {@code splits} methods support parallelisation
	* and are robust against accidental correlation by using unique values for the additive parameter
	* for each instance in the same stream. The primitive streaming methods support parallelisation
	* but with no assurances of accidental correlation; each thread uses a new instance with a
	* randomly initialised state.
	*
	* @see <a href="https://doi.org/10.1145/3485525">Steele & Vigna (2021) Proc. ACM Programming
	* Languages 5, 1-31</a>
	* @see <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/random/package-summary.html">
	* JDK 17 java.util.random javadoc</a>
	* @since 1.5
	*/
	public class L64X128Mix extends AbstractL64X128 implements SplittableUniformRandomProvider {
	/**
	* Creates a new instance.
	*
	* @param seed Initial seed.
	* If the length is larger than 4, only the first 4 elements will
	* be used; if smaller, the remaining elements will be automatically
	* set. A seed containing all zeros in the last two elements
	* will create a non-functional XBG sub-generator and a low
	* quality output with a period of 2<sup>64</sup>.
	*
	* <p>The 1st element is used to set the LCG increment; the least significant bit
	* is set to odd to ensure a full period LCG. The 2nd element is used
	* to set the LCG state.</p>
	*/
	public L64X128Mix(long[] seed) {
	super(seed);
	}

	/**
	* Creates a new instance using a 4 element seed.
	* A seed containing all zeros in the last two elements
	* will create a non-functional XBG sub-generator and a low
	* quality output with a period of 2<sup>64</sup>.
	*
	* <p>The 1st element is used to set the LCG increment; the least significant bit
	* is set to odd to ensure a full period LCG. The 2nd element is used
	* to set the LCG state.</p>
	*
	* @param seed0 Initial seed element 0.
	* @param seed1 Initial seed element 1.
	* @param seed2 Initial seed element 2.
	* @param seed3 Initial seed element 3.
	*/
	public L64X128Mix(long seed0, long seed1, long seed2, long seed3) {
	super(seed0, seed1, seed2, seed3);
	}

	/**
	* Creates a copy instance.
	*
	* @param source Source to copy.
	*/
	protected L64X128Mix(L64X128Mix source) {
	super(source);
	}

	/** {@inheritDoc} */
	@Override
	public long next() {
	// LXM generate.
	// Old state is used for the output allowing parallel pipelining
	// on processors that support multiple concurrent instructions.

	final long s0 = x0;
	final long s = ls;

	// Mix
	final long z = LXMSupport.lea64(s + s0);

	// LCG update
	ls = M * s + la;

	// XBG update
	long s1 = x1;

	s1 ^= s0;
	x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b
	x1 = Long.rotateLeft(s1, 37); // c

	return z;
	}

	/** {@inheritDoc} */
	@Override
	protected L64X128Mix copy() {
	// This exists to ensure the jump function performed in the super class returns
	// the correct class type. It should not be public.
	return new L64X128Mix(this);
	}

	/** {@inheritDoc} */
	@Override
	public SplittableUniformRandomProvider split(UniformRandomProvider source) {
	return create(source.nextLong(), source);
	}

	/** {@inheritDoc} */
	@Override
	public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) {
	return RandomStreams.generateWithSeed(streamSize, source, L64X128Mix::create);
	}

	/**
	* Create a new instance using the given {@code seed} and {@code source} of randomness
	* to initialise the instance.
	*
	* @param seed Seed used to initialise the instance.
	* @param source Source of randomness used to initialise the instance.
	* @return A new instance.
	*/
	private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) {
	// LCG state. The addition uses the input seed.
	// The LCG addition parameter is set to odd so left-shift the seed.
	final long s0 = seed << 1;
	final long s1 = source.nextLong();
	// XBG state must not be all zero
	long x0 = source.nextLong();
	long x1 = source.nextLong();
	if ((x0 \| x1) == 0) {
	// SplitMix style seed ensures at least one non-zero value
	x0 = LXMSupport.lea64(s1);
	x1 = LXMSupport.lea64(s1 + LXMSupport.GOLDEN_RATIO_64);
	}
	return new L64X128Mix(s0, s1, x0, x1);
	}
	}